I. Field of the Invention
The present invention concerns character recognition.
II. Related Art and Other Considerations
Japanese Laid-Open Patent Publication No. 2-206894 proposes a character recognition method that recognizes characters of, e.g., a license plate of an automobile by binarizing an image of character areas on the license plate and seeking a 4-digit serial number composed of relatively large characters included in the binary image by key features (e.g., width of characters and gap between characters) of the license plate.
Japanese Laid-Open Patent Publication No. 6-131492 proposes a character recognition method that searches an area by relative positions determined from information on position of a 4-digit serial number and then recognizes characters in each of the determined character areas.
In the former method it is difficult to accurately determine the position of a serial number if any positional information on any digit of the 4-digit serial number could not correctly be obtained due to (1) noise caused by an incorrect positioning or conditioning of an image-taking camera or (2) the obtained serial number containing only 1 digit or 2 digits, i.e., a reduced number of large-size characters.
The latter method also requires the accurate determination of the serial number because its location is a key to determine areas of the other character areas. For example, in this latter method it is difficult to correctly presume character areas in an image of a license plate if the input image lacks a part of a license plate or does not indicate a part of a serial number due to an obstruction or it includes noise signals caused by both side frames, an indicator lamp and so on.